The invention relates to the field of optical disk data storage and retrieval.
The invention relates to an optical disc including a recording area for recording data at a substantially constant density, the recording area being subdivided in a plurality of coaxial annular zones including circular or spiral tracks, each track within one of the zones for storing a same predetermined amount of data at a track density, the average of the track densities within one zone being substantially equal to the constant density.
The invention further relates to a recording device for recording data at a substantially constant density on an optical disc including a recording area having circular or spiral tracks, which recording area is subdivided in a plurality of coaxial annular zones, which device includes a recording head and recording control apparatus.
The invention further relates to a read device for reading data from an optical disc recorded at a substantially constant density, the optical disc including a recording area having circular or spiral tracks, which recording area is subdivided in a plurality of coaxial annular zones, which device includes a reading head and read control means.
Such a record carrier and apparatus are known from European Patent Application EP 0 587 019, herein document D1. The document discloses a record carrier in the form of an optical disc having a recording area including a pattern of grooves on a substrate, constituting a servopattern of circular or spiral tracks. The recording area is subdivided in coaxial annular zones, and within a zone each track includes the same amount of data. Hence the density of data storage decreases when going radially outward, whereas at the start of the next zone the density is restored. The average density over the entire surface is substantially equal, usually called a CLV (Constant Linear Velocity) density, e.g. as used in the audio CD. However within a zone the amount of data in each turn of the track is constant, usually called a CAV density (Constant Angular Velocity). The disc comprises a number of radially aligned servo pits in each turn, constituting a so-called sampled servo pattern. The servo pattern including radially aligned elements is called Constant Angular Velocity (CAV) servo pattern, and is to be scanned by a servo system having a phase locked loop (PLL) to generate a servo frequency locked to the rotation frequency of the disc. The servo pits are dimensioned to be read clocked by said servo frequency. Further a data phase locked loop is provided for generating a data clock locked to a speed of data read/write operations, which are performed at the substantially constant linear density. When jumping to a new radial position, the rotation frequency setting point or the data clock setting point are adjusted to the new position, but the servo phase locked loop remains locked to the CAV servo pattern. Hence the servo pits are always read at the servo frequency. The recording apparatus including an optical system for recording or reading information by generating a spot via a radiation beam on a track of the record carrier. The optical disc is rotated and the spot is positioned in radial direction on the centre of the track by servo means for scanning the track. During scanning the servo phase locked loop is locked to the rotation frequency of the disc for reading the CAV servo pattern. The data phase locked loop is locked to the CLV data speed. The known record carrier and apparatus have the problem, that for reliable operation a first phase locked loop must be locked to the CAV servo pattern, and a second phase locked loop must be locked to the CLV data density. Those skilled in the art are also directed to U.S. Pat. 4,901,300, herein document D2.
The above references are hereby incorporated herein in whole by reference.
It is an object of the invention to provide an optical disc, a recording and a reading device arranged for a more reliable data recording and/or retrieval operation while data is recorded at a substantially constant density.
An optical disc has tracks that include periodic characteristics which are radially aligned within each one of the zones, the periodicity being indicative of the track recording density for the track concerned. This has the effect, that the speed of data recording and reading can be directly locked to a signal generated by detecting the periodic characteristics. When jumping within a zone the speed is not changed, whereas when jumping to a different zone the speed changes by a known amount. There is no need for a second phase locked loop, only one phase locked loop locked to the data frequency is required. Hence, the recording is less complex and more reliable.
A recording device has recording control apparatus arranged for detecting the periodic characteristics and for recording depending thereon a same predetermined amount data in each track within one of the zones at said track density. A reading device has read control apparatus arranged for detecting the periodic characteristics and for reading depending thereon a same predetermined amount data from each track within one of the zones at the track density. This has the effect, that data, although positioned corresponding to a CAV pattern within a zone, has on average substantially the CLV density, and can be recorded and read by apparatus directly synchronized to a signal generated by detecting the periodic characteristics.
The invention is also based on the following recognition relating to the reliability of the detection of servo signals in high density optical recording. For achieving the high density the distance between tracks, the track pitch, is designed as small as possible for the available scanning system and scanning spot size. When servo elements, e.g. pits or other periodic track characteristics, are then scanned and a servo signal is generated, the servo elements of neighbouring tracks also influence the servo signal, which is called cross-talk. However for a CLV density the amount of data stored in a track must be increased radially. The inventors have seen that by aligning the periodic characteristics within a zone the cross-talk within the zone can be eliminated. At the start of the next zone the density is increased stepwise, so that on average the density is substantially equal to the CLV density. The cross-talk problem is now only present at the boundary track between two zones. The boundary track can be skipped, or special countermeasures can be taken to control the interference problems at the zone boundary.
In an embodiment of the optical disc, is the size of zones is such that the difference in the number of periodic characteristics in a turn of the track at the boundaries of adjoining zones is relatively low in relation to the number of periodic characteristics in a turn of the track. A difference in periodicity causes an interference pattern including (partial) extinctions in a boundary signal generated from the periodic characteristics when scanning a track at the boundary of two zones. A low difference in relation to the periodicity results in the boundary signal having only a few extinctions, which can be positioned by selecting the phase difference of the periodic characteristics.